Articles of footwear usually include an upper, a midsole, and an outsole. The upper can include sections of thin material, straps, or the like for securing the footwear to the wearer's foot. The outsole is typically a unitary piece of relatively high-friction material that provides traction for the footwear. Also, the midsole can be a unitary piece of foam or other similar material disposed between the upper and the outsole for providing cushioned support for the wearer.
The midsole can be designed in various ways according to the intended use of the wearer to provide a desired type of cushioning. For example, footwear for long distance running can have a midsole that is thicker toward the heel of the foot as compared to the ball of the foot to thereby provide greater cushioning to the heel since running activity imparts increased shock primarily to this area of the foot. In addition, different midsoles can be made out of different materials, each having a different resistance to resilient deformation (e.g., a different durometer), and the material can be selected according to the intended use of the footwear to provide the desired type of cushioning.
Also, the outsole can be similarly refined. For instance, the outsole intended for running on an indoor track can be smoother than an outsole intended for running in the outdoors.
Although conventional midsoles and outsoles have been adequate for their intended purposes, they do suffer from certain disadvantages. For instance, because the typical midsole and outsole are both single, unitary pieces of material that are fixed together, the footwear can be less versatile and/or adaptable. More specifically, it can be difficult to alter a specific zone of the midsole and/or outsole once that zone has been designed for a particular article of footwear.
In addition, because the outsole is commonly fixed to the midsole, the outsole can limit or otherwise affect the mode of flexing of the midsole. For instance, the outsole can be made out of rubber and the midsole can be made out of foam. Thus, because the rubber material is more resistant to flexing, the outsole will usually inhibit the foam midsole from flexing. Accordingly, the footwear may not provide sufficient support for the wearer.